How Krytox Meets the Mil-Spec Standards for Lubrication

Mil Spec Lubricant Krytox

Military Specification Lubrication | Mil-Spec Lubrication

A United States defense standard, often called a military standard, “MIL-STD“, “MIL-SPEC“, or (informally) “MilSpecs“, is used to help achieve standardization objectives by the U.S. Department of Defense. Standardization is beneficial in achieving interoperability, ensuring products meet certain requirements, commonality, reliability, the total cost of ownership, compatibility with logistics systems, and similar defense-related objectives.

Specialized MIL-Specs (MIL-PRF-27617) were developed to cover the requirements for greases resistant to hydrocarbon fuel and liquid oxygen specifically applicable in aircraft, aerospace vehicles, and supporting equipment. These fuel resistant greases are intended for use in the lubrication of taper plug valves, gaskets, and bearings in fuel systems of aircraft and ground support equipment. It is also suitable for use in the presence of liquid oxygen as a lubricant for valves, threads, and bearings in aerospace vehicles. Within the MIL-PRF-27617 there are delineations into sub-types,  Type I-V.  These ‘Types’ have specified parameters and performance metrics defined within them that lubricants must meet to be utilized in applications which call for that MIL-SPEC Type.

Defense standards are also used by other nondefense government organizations, technical organizations, and industry. This article discusses definitions, history, and usage of defense standards. Related documents, such as defense handbooks and defense specifications, are also addressed.


MIL-PRF-27617 Type I performance lubricant requirements typically require lower temperature range and lower viscosity greases and are not designed for high-temperature applications. However, they exhibit high penetration, no oil separation, and complete oxygen stability. An excellent representation of a lubricant which excels within this MIL-SPEC is Krytox™ 240AZ. 


MIL-SPEC PRF 27617 Type II lubricants have increased temperature stability range from -40 to 204 C and offer exceptional chemical and thermal stability, minimal evaporation, low hydrocarbon fuel solubility, and <20% water-washout while providing NGLI 2 penetration.  One of the highest-performing lubricants which conform to the Type II specifications is Krytox™ 240AB.


MIL-SPEC 27617 Type III greases exhibit NLGI 2 penetration, extremely high temperature, and oxidation stability, <20% solubility in a hydrocarbon fuel, and minimal evaporation at 200 C. An industry standard which exceeds all of these metrics and is well-known for offering unmatched performance is Krytox™ 240AC.


MIL-SPEC PRF 26717 Type IV greases must exhibit minimal evaporation,  low fuel solubility, complete oxygen stability, offer excellent resistance to extreme pressure over wide temperature range, and modest changes in worked vs unworked penetrations. Known for its unsurpassed performance, Krytox™ FPG 028 delivers top-tier performance in all critical physical properties and is designed to operate under severe conditions, and can be used for bearings, gears, and as a lubricant for O-rings and elastomers.


The recommendation made here with and the information set forth with respect to the performance or use of our products are believed, but not warranted to be accurate. The products discussed are sold without warranty, as to fitness or performance, express or implied and upon condition that purchasers shall make their own test to determine suitability of such products for their particular purposes. Likewise, statements concerning the possible uses of our products are not intended as recommendations to use our products in the infringement of any patent.